We are thinking about promoting a competition to help launch our mobile game.
The prizepool will be ~$10,000 USD and it will be free to enter.
It will be available worldwide and the winner will be paid through PayPal.

The winners will be decided based on skill - how well they score in our game.
We will verify results through Apple's Game Center.

My question is:Is this legal and are there any fees/forms/certificates I need to attain to promote this competition?